1. Field of the Invention
The present invention relates to the field of semiconductor technology, and more particularly to an LED backlight driving circuit and a backlight module.
2. Description of Related Art
The LCD display panel cannot generate the light source, and it have to use backlight method to project the light onto the display panel such that the display panel generate the brightness, and the brightness is uniformly distributed in order to display a picture. At present, the backlight source of the LCD display panel uses the LED or the CCFL. Comparing to the CCFL for the backlight source, the LED backlight source has the advantages of low power consumption, long life, ultra-thin and good optical characteristic, etc. Therefore, the liquid crystal display using white LED as the backlight source gradually becomes the development direction of the LCD TV.
In order to ensure the performance of the LED backlight module and to avoid the failure of the LED backlight module which causes the LCD device cannot display, the protection mechanism for the LED backlight driving circuit is important. In the LED backlight driving circuit, the output high voltage is connected to the positive electrode of the LED to drive the LED for emitting light. When the positive and negative electrodes of the LED are shorted, the high output voltage will directly enter the LED constant current driving IC and other parts from the negative electrode of the LED, so that it cause the parts being burned out, which causes the LED backlight driving circuit work abnormally.
In order to solve the above problems, as shown in FIG. 1, in the prior art, an isolation MOS (Metal-Oxide-Semiconductor, a field effect transistor) is usually added to the negative electrode of the LED. The source of the MOS is connected to the negative electrode of the LED. The drain is connected to the LED constant current driving IC. The gate is connected to an external DC working voltage to control the MOS transistor to conduct when the LED backlight driving circuit is operating normally. When the positive and negative electrodes of the LED are shorted, the source voltage of the MOS is higher than the gate voltage such that the MOS is disconnected in order to prevent the high voltage enter into the LED constant current driving IC as well as the rear parts to protect the entire circuit.
Although the function of the MOS transistor can protect the LED backlight driving circuit, when the LED backlight driving circuit is operating normally, the MOS transistor is turned, the larger power loss occurs at the MOS transistor. And the temperature of the MOS transistor is higher, which affects its life. Furthermore, the price of the MOS transistor is higher, which is not conducive to cost reduction. In addition, when MOS transistor is disconnected, the negative electrode of the LED still exist a high voltage, which will cause some security risks.